1. Field of the Invention
One embodiment of the invention generally relates to fabrication of analog integrated circuit. In particular, one embodiment the invention relates to trimming of analog current references, which is typically performed during test of an integrated circuit.
2. Description of the Related Art
Unlike digital circuits, analog circuits frequently use adjustment or trimming procedures. One such analog circuit is a current reference. Current references are frequently used in analog integrated circuits. These current references can be either current sources or current sinks. In practice, current references can be relatively difficult to implement. For example, a current reference should be of relatively high precision when used as a reference for a digital-to-analog converter (DAC). Otherwise, the analog output of the DAC can become degraded.
In one conventional current reference, the reference current is generated by mirroring an initial reference current. Due to the relatively large variability from die to die of resistors, the initial reference current is trimmed by trimming the resistors. However, these resistor trims can affect other biases, thus requiring further trimming in mirroring references. These other trimming operations can require additional components, such as trimming DACs and extra mirrors for each current reference. The additional circuits can increase die area, cost, and power consumption. In addition, the additional trimming procedures, often requiring trimming of each current reference, can be relatively time consuming, which adds to production test time and cost. The additional expense becomes particularly acute when relatively many current references are present. For example, it is not uncommon to have 32 current references on an integrated circuit for references or biasing of other circuits.